Aldehyde dehydrogenase 3 converts farnesal into farnesoic acid in the corpora allata of mosquitoes

Genome of tropical bed bug Cimex hemipterus (Cimicidae, Hemiptera) reveals tetraspanin expanded in bed bug ancestor

Cimex species are ectoparasites that exclusively feed on warm-blooded animals such as birds and mammals. Three cimicid species are known to be persistent pests for humans, including the tropical bed bug Cimex hemipterus, common bed bug Cimex lectularius, and Eastern bat bug Leptocimex boueti. To date, genomic information is restricted to the common bed bug C. lectularius, which limits understanding their biology and to provide controls of bed bug infestations. Here, a chromosomal-level genome assembly of C. hemipterus (495 Mb [megabase pairs]) contained on 16 pseudochromosomes (scaffold N50 = 34 Mb), together with 9 messenger RNA and small RNA transcriptomes were obtained. In comparison between hemipteran genomes, we found that the tetraspanin superfamily was expanded in the Cimex ancestor. This study provides the first genome assembly for the tropical bed bug C. hemipterus, and offers an unprecedented opportunity to address questions relating to bed bug infestations, as well as genomic evolution to hemipterans more widely.

Investigating the role of aae-miR-34-5p in the regulation of juvenile hormone biosynthesis genes in the mosquito Aedes aegypti

Juvenile hormone (JH) controls the development and reproduction of insects. Therefore, a tight regulation of the expression of JH biosynthetic enzymes is critical. microRNAs (miRNAs) play significant roles in the post-transcriptional regulation of gene expression by interacting with complementary sequences in target genes. Previously, we reported that several miRNAs were differentially expressed during three developmental stages of Aedes aegypti mosquitoes with different JH levels (no JH, high JH, and low JH). One of these miRNAs was aae-miR-34-5p. In this study, we identified the presence of potential target sequences of aae-miR-34-5p in the transcripts of some genes encoding JH biosynthetic enzymes. We analysed the developmental expression patterns of aae-miR-34-5p and the predicted target genes involved in JH biogenesis. Increases in miRNA abundance were followed, with a delay, by decreases in transcript levels of target genes. Application of an inhibitor and a mimic of aae-miR-34-5p led respectively to increased and decreased levels of thiolase transcripts, which is one of the early genes of JH biosynthesis. Female adult mosquitoes injected with an aae-miR-34-5p inhibitor exhibited significantly increased transcript levels of three genes encoding JH biosynthetic enzymes, acetoacetyl-CoA thiolase (thiolase), farnesyl diphosphate phosphatase, and farnesal dehydrogenase. Overall, our results suggest a potential role of miRNAs in JH production by directly targeting genes involved in its biosynthesis.

New insights into the regulation mechanism of Pacific white shrimp (Litopenaeus vannamei) hepatopancreas under 4-nonylphenol exposure using transcriptome analysis

4-Nonylphenol (4-NP) is one of the common endocrine-disrupting chemicals (EDCs) in estuaries and coastal zones, which can exert detrimental effects on the physiological function of aquatic organisms. However, the molecular response triggered by 4-NP remains largely unknown in Pacific white shrimp (Litopenaeus vannamei). In this study, transcriptomic analysis was performed to investigate the underlying mechanisms of 4-NP toxicity in the hepatopancreas of L. vannamei. Nine RNA-Seq libraries were generated from L. vannamei at 0 h, 24 h, and 48 h following exposure to 4-NP. Compared with 0 h vs 24 h, 962 up- and 463 down-regulated differentially expressed genes (DEGs) were identified, indicating that many genes in L. vannamei were induced to resist adverse circumstances by 4-NP exposure. In contrast, 902 up- and 1027 down-regulated DEGs were revealed in the comparison of 0 h vs 48 h, demonstrating that prolonged exposure to the stress from 4-NP resulted in more inhibited genes. To validate the accuracy of the transcriptome data, eight DEGs were selected for quantitative real-time polymerase chain reaction (qRT-PCR), which were consistent with the RNA-Seq results. Through KEGG pathway enrichment analysis, three specific pathways related to hormonal effects and endocrine function of L. vannamei were enriched significantly, including tyrosine metabolism, insect hormone biosynthesis, and melanogenesis. After 4-NP stress, genes involved in tyrosine metabolism (Tyr) and melanogenesis pathway (AC, CBP, Wnt, Frizzled, Tcf, and Ras) were induced to promote melanin pigment to help shrimp resist adverse environments. In the insect hormone biosynthesis, ALDH, CYP15A1, CYP15A1/C1, and JHE genes were activated to synthesize juvenile hormone (JH), while Spook, Phm, Sad, and CYP18A1 were induced to generate molting hormone. There is an enhanced interaction between the molting hormone and JH, with JH playing a dominant role and maintaining its "classic status quo action". Our study demonstrated that 4-NP exposure led to impairments of biological functions in L. vannamei hepatopancreas. The genes and pathways identified provide novel insights into the molecular mechanisms underlying 4-NP toxicity effects in prawns and enrich the information on the toxicity mechanism of crustaceans in response to EDCs exposure.

Differential venom gland gene expression analysis of juvenile and adult scorpions Androctonus crassicauda

Background

The Androctonus crassicauda, belonging to the genus Androctonus of the family Buthidae, is the most venomous scorpion in Middle East countries. However, the venom gland transcriptome profile of A. crassicauda scorpion has not yet been studied. In this study, we elucidated and compared the venom gland gene expression profiles of adult and juvenile male scorpion A. crassicauda using high-throughput transcriptome sequencing. This is the first report of transcriptional analysis of the venom glands of scorpions in different growth stages, with insights into the identification of the key genes during venom gland development.

Results

A total of 209,951 mRNA transcripts were identified from total RNA-seq data, of which 963 transcripts were differentially expressed (DE) in adult and juvenile scorpions (p < 0.01). Overall, we identified 558 up-regulated and 405 down-regulated transcripts in the adult compared to the juvenile scorpions, of which 397 and 269 unique unigenes were annotated, respectively. GO and KEGG enrichment analyses indicated that the metabolic, thermogenesis, cytoskeleton, estrogen signaling, GnRH signaling, growth hormone signaling, and melanogenesis pathways were affected by two different growth conditions and the results suggested that the DE genes related to those pathways are important genes associated with scorpion venom gland development, in which they may be important in future studies, including Chs, Elovl, MYH, RDX, ACTN, VCL, PIP5K, PP1C, FGFR, GNAS, EGFR, CREB, CoA, PLCB, CALM, CACNA, PKA and CAMK genes.

Conclusions

These findings broadened our knowledge of the differences between adult and juvenile scorpion venom and opened new perspectives on the application of comparative transcriptome analysis to identify the special key genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08866-1.

Systematic analysis of olfactory protein-protein interactions network of fruitfly, Drosophila melanogaster

Olfaction is one of the physiological traits of insect behavior. Insects have evolved a sophisticated olfactory system and use a combined coding strategy to process general odor. Drosophila melanogaster is a powerful model to reveal the molecular and cellular mechanisms of odor detection. Identifying new olfactory targets through complex interactions will contribute to a better understanding of the functions, interactions, and signaling pathways of olfactory proteins. However, the mechanism of D. melanogaster olfaction is still unclear, and more olfactory proteins are required to be discovered. In this study, we tried to explore essential proteins in the olfactory system of D. melanogaster and conduct protein-protein interactions (PPIs) analysis. We constructed the PPIs network of the olfactory system of D. melanogaster, consisting of 863 proteins and 18,959 interactions. Various methods were used to perform functional enrichment analysis, topological analysis and cluster analysis. Our results confirmed that Class B scavenger receptors (SR-Bs), glutathione S-transferases (GSTs), and UDP-glycosyltransferases (UGTs) play an essential role in olfaction of D. melanogaster. The proteins obtained in this study can be used for subsequent functional identification in D. melanogaster olfactory.

Rethinking Sesquiterpenoids: A Widespread Hormone in Animals

The sesquiterpenoid hormone juvenile hormone (JH) controls development, reproduction, and metamorphosis in insects, and has long been thought to be confined to the Insecta. While it remains true that juvenile hormone is specifically synthesized in insects, other types or forms of sesquiterpenoids have also been discovered in distantly related animals, such as the jellyfish. Here, we combine the latest literature and annotate the sesquiterpenoid biosynthetic pathway genes in different animal genomes. We hypothesize that the sesquiterpenoid hormonal system is an ancestral system established in an animal ancestor and remains widespread in many animals. Different animal lineages have adapted different enzymatic routes from a common pathway, with cnidarians producing farnesoic acid (FA); non-insect protostomes and non-vertebrate deuterostomes such as cephalochordate and echinoderm synthesizing FA and methyl farnesoate (MF); and insects producing FA, MF, and JH. Our hypothesis revolutionizes the current view on the sesquiterpenoids in the metazoans, and forms a foundation for a re-investigation of the roles of this important and yet neglected type of hormone in different animals.

Comparative Transcriptome Analysis Reveals Molecular Insights in Overwintering Monochamus alternatus (Coleoptera: Cerambycidae)

Monochamus alternatus, the dominant vector of Bursaphelenchus xylophilus (Aphelenchida: Aphelenchoididae), has caused immense damage to forest resources. In China, this vector was native to the southern regions but has spread northward recently. To adapt to more challenging environments in the northern winter, M. alternatus has evolved an intricate strategy for overwintering, which remains largely unknown. Herein, we compared the transcriptome data of the overwintering and non-overwintering larvae of M. alternatus larvae to investigate the molecular mechanisms in overwintering. A total of 53.10 GB clean bases and 28, 245 unigenes were obtained by RNA-seq. Analysis of 2597 upregulated and 2429 downregulated unigenes, as well as the enrichment of DEGs showed that many genes and pathways were jointly involved in the overwintering period. Besides, the accuracy of the RNA-seq data was tested by using qPCR experiment involving 13 selected genes. The results revealed that the overwintering process relied largely on the energy allocation trade-off. Specifically, overwintering M. alternatus inhibited energy-intensive activities, such as growth and molting, detoxification, and trehalose transport, and the reserved energy was skewed towards the synthesis of antifreeze compounds and immune response to cope with the deleterious effects of winter.

Effects of camptothecin on histological structures and gene expression profiles of fat bodies in Spodoptera frugiperda

Spodoptera frugiperda is a serious threat to global food production. Our previous study demonstrated that Camptothecin (CPT), a bioactive secondary metabolite from Camptotheca acuminata (Decne: Nyssaceae), exhibits adverse impact on the larval midgut of S. frugiperda and inhibits insect growth. However, effects of CPT on fat bodies of S. frugiperda larvae have not been examined yet. In the present study, we found that histological structures of fat bodies of S. frugiperda larvae were damaged in insects treated with CPT. Comparative transcriptomic analyses among different fat body samples from controls and insects treated with 1.0 and 5.0 μg/g CPT were performed. A total of 4212 and 5044 differentially expressed genes (DEGs) were identified in the samples treated with 1.0 and 5.0 μg/g CPT, respectively. Our data indicated that the pathways of detoxification, immune response, fatty acids, chitin, and hormone biosynthesis in fat bodies were affected by CPT treatments based on DEGs. These results provided a comprehensive view of the damage and gene expression changes in fat bodies of S. frugiperda after CPT exposure, which shall be useful to reveal the mechanism of CPT toxicity against S. frugiperda in future.

A mitochondrial phosphatase PTPMT1 is essential for the early development of silkworm, Bombyx mori

Juvenile hormone (JH) plays important roles in the control of many biological processes in insects, such as development, reproduction, and polyphenism. JH is primarily produced in the corpora allata (CA) by specific JH biosynthetic enzymes under strict temporal regulation. In a previous study, we identified a novel putative JH biosynthetic gene, protein tyrosine phosphatase, mitochondrial 1 (PTPMT1), from silkworm, Bombyx mori, whose expression is nearly exclusive in the CA and is correlated with JH synthetic activities during late larval development. In this study, to reveal the function of PTPMT1 in vivo, we generated PTPMT1 knockout silkworms using TALEN. In the knockout mutants, no signs indicating defects in JH activity were observed. Instead, PTPMT1 knockout silkworms showed embryonic lethality, developmental arrest, and 3rd-instar lethality not only in mutants lacking total enzymatic activity but also in mutants lacking mitochondrial translocation signals. Moreover, in PTPMT1 knockout embryos, the expression of two genes encoded by the mitochondrial genome, CYTB and ND3, was decreased, indicating a mitochondrial disorder. These results suggested that PTPMT1 plays conserved vital role(s) reported in vertebrates in insect mitochondria.

The juvenile hormone described in Rhodnius prolixus by Wigglesworth is juvenile hormone III skipped bisepoxide

Juvenile hormones (JHs) are sesquiterpenoids synthesized by the corpora allata (CA). They play critical roles during insect development and reproduction. The first JH was described in 1934 as a “metamorphosis inhibitory hormone” in Rhodnius prolixus by Sir Vincent B. Wigglesworth. Remarkably, in spite of the importance of R. prolixus as vectors of Chagas disease and model organisms in insect physiology, the original JH that Wigglesworth described for the kissing-bug R. prolixus remained unidentified. We employed liquid chromatography mass spectrometry to search for the JH homologs present in the hemolymph of fourth instar nymphs of R. prolixus. Wigglesworth’s original JH is the JH III skipped bisepoxide (JHSB3), a homolog identified in other heteropteran species. Changes in the titer of JHSB3 were studied during the 10-day long molting cycle of 4^th instar nymph, between a blood meal and the ecdysis to 5^th instar. In addition we measured the changes of mRNA levels in the CA for the 13 enzymes of the JH biosynthetic pathway during the molting cycle of 4^th instar. Almost 90 years after the first descriptions of the role of JH in insects, this study finally reveals that the specific JH homolog responsible for Wigglesworth’s original observations is JHSB3.

Reconstruction of insect hormone pathways in an aquatic firefly, Sclerotia aquatilis (Coleoptera: Lampyridae), using RNA-seq

Insect hormones: ecdysteroids and juvenile hormones have crucial functions during the regulation of different developmental pathways in insects. Insect metamorphosis is one of the primary pathways regulated by these hormones. The insect hormone biosynthetic pathway is conserved among arthropods, including insects, with some variations in the form of hormones used among each group of insects. In this study, the candidate genes involved in the insect hormone pathways and their functional roles were assessed in an aquatic firefly, Sclerotia aquatilis using a high-throughput RNA sequencing technique. Illumina next-generation sequencing (NGS) was used to generate transcriptome data for the different developmental stages (i.e., larva, pupa, and adult) of S. aquatilis. A total of 82,022 unigenes were generated across all different developmental stages. Functional annotation was performed for each gene, based on multiple biological databases, generating 46,230 unigenes. These unigenes were subsequently mapped using KEGG pathways. Accordingly, 221 protein-encoding genes involved in the insect hormone pathways were identified, including, JHAMT, CYP15A1, JHE, and Halloween family genes. Twenty potential gene candidates associated with the biosynthetic and degradation pathways for insect hormones were subjected to real-time PCR, reverse transcriptase PCR (RT-PCR) and sequencing analyses. The real-time PCR results showed similar expression patterns as those observed for transcriptome expression profiles for most of the examined genes. RT-PCR and Sanger sequencing confirmed the expressed coding sequences of these gene candidates. This study is the first to examine firefly insect hormone pathways, facilitating a better understanding of firefly growth and development.

Transgenerational response to early spring warming in Daphnia

Temperature and photoperiod regulate key fitness traits in plants and animals. However, with temperature increase due to global warming, temperature cue thresholds are experienced at shorter photoperiods, disrupting the optimal seasonal timing of physiological, developmental and reproductive events in many species. Understanding the mechanisms of adaptation to the asynchrony between temperature and photoperiod is key to inform our understanding of how species will respond to global warming. Here, we studied the transgenerational mechanisms of responses of the cyclical parthenogen Daphnia magna to different photoperiod lengths co-occurring with warm temperature thereby assessing the impact of earlier spring warming on its fitness. Daphnia uses temperature and photoperiod cues to time dormancy, and to switch between sexual and asexual reproduction. Daphnia life cycle offers the opportunity to measure the relative contribution of plastic and genetic responses to environmental change across generations and over evolutionary time. We use transgenerational common garden experiments on three populations 'resurrected' from a biological archive experiencing temperature increase over five decades. Our results suggest that response to early spring warming evolved underpinned by a complex interaction between plastic and genetic mechanisms while a positive maternal contribution at matching environments between parental and offspring generation was also observed.

Ecdysteroid and juvenile hormone biosynthesis, receptors and their signaling in the freshwater microcrustacean Daphnia

The two essential insect hormones, ecdysteroids and juvenile hormones, are possessed not only by insects, but also widely by arthropods, and regulate various developmental and physiological processes. In contrast to the abundant information about molecular endocrine mechanisms in insects, the knowledge of non-insect arthropod endocrinology is still limited. In this review, we summarize recent reports about the molecular basis of these two major insect hormones in the freshwater microcrustacean Daphnia, a keystone taxon in limnetic ecology and a bioindicator in environmental studies. Comprehensive comparisons of endocrine signaling pathways between insects and daphnids may shed light on the regulatory mechanisms of various biological phenomena and, moreover, evolutionary processes of arthropod species.

Omics approaches to study juvenile hormone synthesis

The juvenile hormones (JHs) are a family of insect acyclic sesquiterpenoids produced by the corpora allata (CA), a pair of endocrine glands connected to the brain. They are involved in the regulation of development, reproduction, behavior, caste determination, diapause, stress response, and numerous polyphenisms. In the post-genomics era, comprehensive analyses using functional 'omics' technologies such as transcriptomics, proteomics and metabolomics have increased our understanding of the activity of the minute CA. This review attempts to summarize some of the 'omics' studies that have contributed to further understand JH synthesis in insects, with an emphasis on our own research on the mosquito Aedes aegypti.

A comparative analysis of corpora allata-corpora cardiaca microRNA repertoires revealed significant changes during mosquito metamorphosis

The corpora allata (CA) are a pair of endocrine glands with neural connections to the brain and close association with another neuroendocrine organ, the corpora cardiaca (CC). The CA from adult female Aedes aegypti mosquitoes synthesize fluctuating levels of juvenile hormone (JH), which have been linked to the ovarian development and are influenced by nutritional signals. In this study, we investigated the potential involvement of microRNAs (miRNAs), a type of small non-coding RNAs, in the regulation of gene expression in CA-CC complexes during mosquito reproductive development, at stages with distinct JH biosynthesis patterns. We analyzed the miRNA repertoires expressed in the CA-CC of pupae, sugar-fed and blood-fed female Ae. aegypti. In total, 156 mature miRNAs were detected in the CA-CC, with 84 displaying significant differences in expression among the three CA-CC developmental stages. There were more miRNAs that were expressed in pupae, and decreased or were absent after adult emergence, when compared with changes between CA-CC of sugar and blood-fed females. Analysis of the genes identified as potential targets for the CA-CC miRNA repertoires classified them into the broad categories of metabolism, information storage and processing, and cellular processes and signaling; with genes involved in cellular processes and signaling representing the largest portion. Among them, the signal-transduction mechanisms and intracellular trafficking, secretion and vesicular transport contained almost 55% of the genes' targets. A substantial number of miRNAs were differentially abundant in the libraries of the three developmental stages, and those changes were much more notable when pupae and adult stages were compared. We detected putative binding sites for some of the most abundant miRNAs on genes encoding JH biosynthetic enzymes and CC neuropeptides. These studies should help us to gain a better understanding of the regulation of CA-CC activity mediated by miRNAs during major developmental stages in mosquitoes.

A reference gene set for sex pheromone biosynthesis and degradation genes from the diamondback moth, Plutella xylostella, based on genome and transcriptome digital gene expression analyses

Background

Female moths synthesize species-specific sex pheromone components and release them to attract male moths, which depend on precise sex pheromone chemosensory system to locate females. Two types of genes involved in the sex pheromone biosynthesis and degradation pathways play essential roles in this important moth behavior. To understand the function of genes in the sex pheromone pathway, this study investigated the genome-wide and digital gene expression of sex pheromone biosynthesis and degradation genes in various adult tissues in the diamondback moth (DBM), Plutella xylostella, which is a notorious vegetable pest worldwide.

Results

A massive transcriptome data (at least 39.04 Gb) was generated by sequencing 6 adult tissues including male antennae, female antennae, heads, legs, abdomen and female pheromone glands from DBM by using Illumina 4000 next-generation sequencing and mapping to a published DBM genome. Bioinformatics analysis yielded a total of 89,332 unigenes among which 87 transcripts were putatively related to seven gene families in the sex pheromone biosynthesis pathway. Among these, seven [two desaturases (DES), three fatty acyl-CoA reductases (FAR) one acetyltransferase (ACT) and one alcohol dehydrogenase (AD)] were mainly expressed in the pheromone glands with likely function in the three essential sex pheromone biosynthesis steps: desaturation, reduction, and esterification. We also identified 210 odorant-degradation related genes (including sex pheromone-degradation related genes) from seven major enzyme groups. Among these genes, 100 genes are new identified and two aldehyde oxidases (AOXs), one aldehyde dehydrogenase (ALDH), five carboxyl/cholinesterases (CCEs), five UDP-glycosyltransferases (UGTs), eight cytochrome P450 (CYP) and three glutathione S-transferases (GSTs) displayed more robust expression in the antennae, and thus are proposed to participate in the degradation of sex pheromone components and plant volatiles.

Conclusions

To date, this is the most comprehensive gene data set of sex pheromone biosynthesis and degradation enzyme related genes in DBM created by genome- and transcriptome-wide identification, characterization and expression profiling. Our findings provide a basis to better understand the function of genes with tissue enriched expression. The results also provide information on the genes involved in sex pheromone biosynthesis and degradation, and may be useful to identify potential gene targets for pest control strategies by disrupting the insect-insect communication using pheromone-based behavioral antagonists.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3592-y) contains supplementary material, which is available to authorized users.

Modeling the flux of metabolites in the juvenile hormone biosynthesis pathway using generalized additive models and ordinary differential equations

Juvenile hormone (JH) regulates development and reproductive maturation in insects. The corpora allata (CA) from female adult mosquitoes synthesize fluctuating levels of JH, which have been linked to the ovarian development and are influenced by nutritional signals. The rate of JH biosynthesis is controlled by the rate of flux of isoprenoids in the pathway, which is the outcome of a complex interplay of changes in precursor pools and enzyme levels. A comprehensive study of the changes in enzymatic activities and precursor pool sizes have been previously reported for the mosquito Aedes aegypti JH biosynthesis pathway. In the present studies, we used two different quantitative approaches to describe and predict how changes in the individual metabolic reactions in the pathway affect JH synthesis. First, we constructed generalized additive models (GAMs) that described the association between changes in specific metabolite concentrations with changes in enzymatic activities and substrate concentrations. Changes in substrate concentrations explained 50% or more of the model deviances in 7 of the 13 metabolic steps analyzed. Addition of information on enzymatic activities almost always improved the fitness of GAMs built solely based on substrate concentrations. GAMs were validated using experimental data that were not included when the model was built. In addition, a system of ordinary differential equations (ODE) was developed to describe the instantaneous changes in metabolites as a function of the levels of enzymatic catalytic activities. The results demonstrated the ability of the models to predict changes in the flux of metabolites in the JH pathway, and can be used in the future to design and validate experimental manipulations of JH synthesis.

Determination of juvenile hormone titers by means of LC-MS/MS/MS and a juvenile hormone-responsive Gal4/UAS system in Aedes aegypti mosquitoes

In anautogenous mosquitoes, juvenile hormone III (JH) plays an essential role in female post-eclosion (PE) development, preparing them for subsequent blood feeding and egg growth. We re-examined the JH titer during the reproductive cycle of female Aedes aegypti mosquitoes. Using liquid chromatography coupled with triple tandem mass spectrometry (LC-MS/MS/MS), we have shown that it reaches its peak at 48-54 h PE in the female hemolymph and at 72 h PE in whole body extracts. This method represents an effective assay for determination of JH titers. The 2.1-kb 5' promoter region of the Early Trypsin (ET) gene, which is specifically expressed in the female midgut under the control of JH during the PE phase, was utilized to genetically engineer the Ae. aegypti mosquito line with the ET-Gal4 activator. We then established the ET-GAL4>UAS-enhanced green fluorescent protein (EGFP) system in Ae. aegypti. In ET-Gal4>UAS-EGFP female mosquitoes, the intensity of the midgut-specific EGFP signal was observed to correspond to the ET gene transcript level and follow the JH titer during the PE phase. The EGFP signal and the EGFP transcript level were significantly diminished in midguts of transgenic female mosquitoes after RNA interference depletion of the JH receptor Methoprene-tolerant (Met), providing evidence of the control of ET gene expression by Met. Topical JH application caused premature enhancement of the EGFP signal and the EGFP transcript level in midguts of newly eclosed ET-Gal4>UAS-EGFP female mosquitoes, in which endogenous JH titer is still low. Hence, this novel ET-Gal4>UAS system permits JH-dependent gene overexpression in the midgut of Ae. aegypti female mosquitoes prior to a blood meal.

Towards a Proteomic Catalogue and Differential Annotation of Salivary Gland Proteins in Blood Fed Malaria Vector Anopheles culicifacies by Mass Spectrometry

In order to understand the importance of functional proteins in mosquito behavior, following blood meal, a baseline proteomic dataset is essential for providing insights into the physiology of blood feeding. Therefore, in this study as first step, in solution and 1-D electrophoresis digestion approach combined with tandem mass spectrometry (nano LC-MS/MS) and computational bioinformatics for data mining was used to prepare a baseline proteomic catalogue of salivary gland proteins of sugar fed An. culicifacies mosquitoes. A total of 106 proteins were identified and analyzed by SEQUEST algorithm against mosquito protein database from Uniprot/NCBI. Importantly, D7r1, D7r2, D7r4, salivary apyrase, anti-platelet protein, calreticulin, antigen 5 family proteins were identified and grouped on the basis of biological and functional roles. Secondly, differential protein expression and annotations between salivary glands of sugar fed vs blood fed mosquitoes was analyzed using 2-Delectrophoresis combined with MALDI-TOF mass spectrometry. The alterations in the differential expression of total 38 proteins was observed out of which 29 proteins like beclin-1, phosphorylating proteins, heme oxygenase 1, ferritin, apoptotic proteins, coagulation and immunity like, serine proteases, serpins, c-type lectin and protein in regulation of blood feeding behavior were found to be up regulated while 9 proteins related to blood feeding, juvenile hormone epoxide hydrolase ii, odorant binding proteins and energy metabolic enzymes were found to be down regulated. To our knowledge, this study provides a first time baseline proteomic dataset and functional annotations of An. culicifacies salivary gland proteins that may be involved during the blood feeding. Identification of differential salivary proteins between sugar fed and blood fed mosquitoes and their plausible role may provide insights into the physiological processes associated with feeding behavior and sporozoite transmission during the process of blood feeding.

Novel NAD+-Farnesal Dehydrogenase from Polygonum minus Leaves. Purification and Characterization of Enzyme in Juvenile Hormone III Biosynthetic Pathway in Plant

Juvenile Hormone III is of great concern due to negative effects on major developmental and reproductive maturation in insect pests. Thus, the elucidation of enzymes involved JH III biosynthetic pathway has become increasing important in recent years. One of the enzymes in the JH III biosynthetic pathway that remains to be isolated and characterized is farnesal dehydrogenase, an enzyme responsible to catalyze the oxidation of farnesal into farnesoic acid. A novel NAD⁺-farnesal dehydrogenase of Polygonum minus was purified (315-fold) to apparent homogeneity in five chromatographic steps. The purification procedures included Gigacap S-Toyopearl 650M, Gigacap Q-Toyopearl 650M, and AF-Blue Toyopearl 650ML, followed by TSK Gel G3000SW chromatographies. The enzyme, with isoelectric point of 6.6 is a monomeric enzyme with a molecular mass of 70 kDa. The enzyme was relatively active at 40°C, but was rapidly inactivated above 45°C. The optimal temperature and pH of the enzyme were found to be 35°C and 9.5, respectively. The enzyme activity was inhibited by sulfhydryl agent, chelating agent, and metal ion. The enzyme was highly specific for farnesal and NAD⁺. Other terpene aldehydes such as trans- cinnamaldehyde, citral and α- methyl cinnamaldehyde were also oxidized but in lower activity. The K_m values for farnesal, citral, trans- cinnamaldehyde, α- methyl cinnamaldehyde and NAD⁺ were 0.13, 0.69, 0.86, 1.28 and 0.31 mM, respectively. The putative P. minus farnesal dehydrogenase that’s highly specific towards farnesal but not to aliphatic aldehydes substrates suggested that the enzyme is significantly different from other aldehyde dehydrogenases that have been reported. The MALDI-TOF/TOF-MS/MS spectrometry further identified two peptides that share similarity to those of previously reported aldehyde dehydrogenases. In conclusion, the P. minus farnesal dehydrogenase may represent a novel plant farnesal dehydrogenase that exhibits distinctive substrate specificity towards farnesal. Thus, it was suggested that this novel enzyme may be functioning specifically to oxidize farnesal in the later steps of JH III pathway. This report provides a basic understanding for recombinant production of this particular enzyme. Other strategies such as adding His-tag to the protein makes easy the purification of the protein which is completely different to the native protein. Complete sequence, structure and functional analysis of the enzyme will be important for developing insect-resistant crop plants by deployment of transgenic plant.

Negative Feedbacks by Isoprenoids on a Mevalonate Kinase Expressed in the Corpora Allata of Mosquitoes

Background

Juvenile hormones (JH) regulate development and reproductive maturation in insects. JHs are synthesized through the mevalonate pathway (MVAP), an ancient metabolic pathway present in the three domains of life. Mevalonate kinase (MVK) is a key enzyme in the MVAP. MVK catalyzes the synthesis of phosphomevalonate (PM) by transferring the γ-phosphoryl group from ATP to the C₅ hydroxyl oxygen of mevalonic acid (MA). Despite the importance of MVKs, these enzymes have been poorly characterized in insects.

Results

We functionally characterized an Aedes aegypti MVK (AaMVK) expressed in the corpora allata (CA) of the mosquito. AaMVK displayed its activity in the presence of metal cofactors. Different nucleotides were used by AaMVK as phosphoryl donors. In the presence of Mg²⁺, the enzyme has higher affinity for MA than ATP. The activity of AaMVK was regulated by feedback inhibition from long-chain isoprenoids, such as geranyl diphosphate (GPP) and farnesyl diphosphate (FPP).

Conclusions

AaMVK exhibited efficient inhibition by GPP and FPP (Ki less than 1 μM), and none by isopentenyl pyrophosphate (IPP) and dimethyl allyl pyrophosphate (DPPM). These results suggest that GPP and FPP might act as physiological inhibitors in the synthesis of isoprenoids in the CA of mosquitoes. Changing MVK activity can alter the flux of precursors and therefore regulate juvenile hormone biosynthesis.

Allatotropin inhibits juvenile hormone biosynthesis by the corpora allata of adult Bombyx mori

Juvenile hormone (JH) synthesis by the corpora allata (CA) does not occur during the pupal stage in both male and female Bombyx mori but begins shortly before adult ecdysis and thereafter only in females. JH biosynthesis in female adults was prevented by allatotropin (AT) through the corpora cardiaca (CC) and the tightly attached oesophagus before adult ecdysis, but after ecdysis, removal of the CC had little effect and only the oesophagus was necessary for AT to prevent JH synthesis. AT could not prevent JH synthesis by the CA alone in either stage. Short neuropeptide F (sNPF) acted directly on the CA, preventing JH biosynthesis without preventing the JH biosynthetic enzymes before adult ecdysis, but had little effect after ecdysis, indicating that the action of AT was not via sNPF. The inhibition of JH synthesis by AT was indirect. Both AT and a factor(s) from the AT-stimulated oesophagus through the CC were necessary for the inhibitory action, which was due to the prevention of some of the JH biosynthetic enzymes. These results clearly show that AT prevents JH synthesis in adult CA in B. mori, although AT stimulates JH biosynthesis by the CA in several insect species.

20-Hydroxyecdysone stimulation of juvenile hormone biosynthesis by the mosquito corpora allata

Juvenile hormone III (JH) is synthesized by the corpora allata (CA) and plays a key role in mosquito development and reproduction. JH titer decreases in the last instar larvae allowing pupation and metamorphosis to progress. As the anti-metamorphic role of JH comes to an end, the CA of the late pupa (or pharate adult) becomes again "competent" to synthesize JH, which plays an essential role orchestrating reproductive maturation. 20-hydroxyecdysone (20E) prepares the pupae for ecdysis, and would be an ideal candidate to direct a developmental program in the CA of the pharate adult mosquito. In this study, we provide evidence that 20E acts as an age-linked hormonal signal, directing CA activation in the mosquito pupae. Stimulation of the inactive brain-corpora allata-corpora cardiaca complex (Br-CA-CC) of the early pupa (24 h before adult eclosion or -24 h) in vitro with 20E resulted in a remarkable increase in JH biosynthesis, as well as increase in the activity of juvenile hormone acid methyltransferase (JHAMT). Addition of methyl farnesoate but not farnesoic acid also stimulated JH synthesis by the Br-CA-CC of the -24 h pupae, proving that epoxidase activity is present, but not JHAMT activity. Separation of the CA-CC complex from the brain (denervation) in the -24 h pupae also activated JH synthesis. Our results suggest that an increase in 20E titer might override an inhibitory effect of the brain on JH synthesis, phenocopying denervation. All together these findings provide compelling evidence that 20E acts as a developmental signal that ensures proper reactivation of JH synthesis in the mosquito pupae.

Characterization of the juvenile hormone pathway in the viviparous cockroach, Diploptera punctata

Juvenile hormones (JHs) are key regulators of insect development and reproduction. The JH biosynthetic pathway is known to involve 13 discrete enzymatic steps. In the present study, we have characterized the JH biosynthetic pathway in the cockroach Diploptera punctata. The effect of exogenous JH precursors on JH biosynthesis was also determined. Based on sequence similarity, orthologs for the genes directly involved in the pathway were cloned, and their spatial and temporal transcript profiles were determined. The effect of shutting down the JH pathway in adult female cockroaches was studied by knocking down genes encoding HMG-CoA reductase (HMGR) and Juvenile hormone acid methyltransferase (JHAMT). As a result, oocyte development slowed as a consequence of reduction in JH biosynthesis. Oocyte length, fat body transcription of Vg and ovarian vitellin content significantly decreased. In addition, silencing HMGR and JHAMT resulted in a decrease in the transcript levels of other genes in the pathway.

Juvenile Hormone Biosynthesis in Insects: What Is New, What Do We Know, and What Questions Remain?

Our understanding of JH biosynthesis has significantly changed in the last years. In this review I would like to discuss the following topics: (1) the progresses in understanding the JH biosynthesis pathway. Access to genome sequences has facilitated the identification of all the genes encoding biosynthetic enzymes and the completion of comprehensive transcriptional studies, as well as the expression and characterization of recombinant enzymes. Now the existence of different flux directionalites, feed-back loops and pathway branching points in the JH biosynthesis pathways can be explored; (2) the new concepts in the modulation of JH synthesis by allatoregulators. The list of putative JH modulators is increasing. I will discuss their possible role during the different physiological states of the CA; (3) the new theoretical and physiological frameworks for JH synthesis analysis. I will discuss the bases of the flux model for JH biosynthesis. JH plays multiple roles in the control of ovary development in female mosquitoes; therefore, the CA presents different physiological states, where JH synthesis is altered by gating the flux at distinctive points in the pathway; (4) in the final section I will identify new challenges and future directions on JH synthesis research.

Metabolic analysis reveals changes in the mevalonate and juvenile hormone synthesis pathways linked to the mosquito reproductive physiology

Juvenile hormone (JH) regulates reproductive maturation in insects; therefore interruption of JH biosynthesis has been considered as a strategy for the development of target-specific insecticides. The corpora allata (CA) from mosquitoes is highly specialized to supply variable levels of JH, which are linked to ovarian developmental stages and influenced by nutritional signals. However, very little is known about how changes in JH synthesis relate to reproductive physiology and how JH synthesis regulation is translated into changes in the CA machinery. With the advent of new methods that facilitate the analysis of transcripts, enzymes and metabolites in the minuscule CA, we were able to provide comprehensive descriptions of the mevalonic (MVA) and JH synthesis pathways by integrating information on changes in the basic components of those pathways. Our results revealed remarkable dynamic changes in JH synthesis and exposed part of a complex mechanism that regulates CA activity. Principal component (PC) analyses validated that both pathways (MVAP and JH-branch) are transcriptionally co-regulated as a single unit, and catalytic activities for the enzymes of the MVAP and JH-branch also changed in a coordinate fashion. Metabolite studies showed that global fluctuations in the intermediate pool sizes in the MVAP and JH-branch were often inversely related. PC analyses suggest that in female mosquitoes, there are at least 4 developmental switches that alter JH synthesis by modulating the flux at distinctive points in both pathways.

Genome-wide comparison of genes involved in the biosynthesis, metabolism, and signaling of juvenile hormone between silkworm and other insects

Juvenile hormone (JH) contributes to the regulation of larval molting and metamorphosis in insects. Herein, we comprehensively identified 55 genes involved in JH biosynthesis, metabolism and signaling in the silkworm (Bombyx mori) as well as 35 in Drosophila melanogaster, 35 in Anopheles gambiae, 36 in Apis mellifera, 47 in Tribolium castaneum, and 44 in Danaus plexippus. Comparative analysis showed that each gene involved in the early steps of the mevalonate (MVA) pathway, in the neuropeptide regulation of JH biosynthesis, or in JH signaling is a single copy in B. mori and other surveyed insects, indicating that these JH-related pathways or steps are likely conserved in all surveyed insects. However, each gene participating in the isoprenoid branch of JH biosynthesis and JH metabolism, together with the FPPS genes for catalyzing the final step of the MVA pathway of JH biosynthesis, exhibited an obvious duplication in Lepidoptera, including B. mori and D. plexippus. Microarray and real-time RT-PCR analysis revealed that different copies of several JH-related genes presented expression changes that correlated with the dynamics of JH titer during larval growth and metamorphosis. Taken together, the findings suggest that duplication-derived copy variation of JH-related genes might be evolutionarily associated with the variation of JH types between Lepidoptera and other insect orders. In conclusion, our results provide useful clues for further functional analysis of JH-related genes in B. mori and other insects.

Starvation increases insulin sensitivity and reduces juvenile hormone synthesis in mosquitoes

Background

The interactions between the insulin signaling pathway (ISP) and juvenile hormone (JH) controlling reproductive trade-offs are well documented in insects. JH and insulin regulate reproductive output in mosquitoes; both hormones are involved in a complex regulatory network, in which they influence each other and in which the mosquito's nutritional status is a crucial determinant of the network's output. Previous studies reported that the insulin-TOR (target of rapamacyn) signaling pathway is involved in the nutritional regulation of JH synthesis in female mosquitoes. The present studies further investigate the regulatory circuitry that controls both JH synthesis and reproductive output in response to nutrient availability.

Methods

We used a combination of diet restriction, RNA interference (RNAi) and insulin treatments to modify insulin signaling and study the cross-talk between insulin and JH in response to starvation. JH synthesis was analyzed using a newly developed assay utilizing fluorescent tags.

Conclusions

Our results reveal that starvation decreased JH synthesis via a decrease in insulin signaling in the corpora allata (CA). Paradoxically, starvation-induced up regulation of insulin receptor transcripts and therefore “primed” the gland to respond rapidly to increases in insulin levels. During this response to starvation the synthetic potential of the CA remained unaffected, and the gland rapidly and efficiently responded to insulin stimulation by increasing JH synthesis to rates similar to those of CA from non-starved females.

Farnesol-like endogenous sesquiterpenoids in vertebrates: the probable but overlooked functional "inbrome" anti-aging counterpart of juvenile hormone of insects?

Literature on the question whether the juvenile stage of vertebrates is hormonally regulated is scarce. It seems to be intuitively assumed that this stage of development is automated, and does not require any specific hormone(s). Such reasoning mimics the state of affairs in insects until it was shown that surgical removal of a tiny pair of glands in the head, the corpora allata, ended larval life and initiated metamorphosis. Decades later, the responsible hormone was found and named "juvenile hormone" (JH) because when present, it makes a larva molt into another larval stage. JH is a simple ester of farnesol, a sesquiterpenoid present in all eukaryotes. Whereas vertebrates do not have an anatomical counterpart of the corpora allata, their tissues do contain farnesol-like sesquiterpenoids (FLS). Some display typical JH activity when tested in appropriate insect bioassays. Some FLS are intermediates in the biosynthetic pathway of cholesterol, a compound that insects and nematodes (=Ecdysozoa) cannot synthesize by themselves. They ingest it as a vitamin. Until a recent (2014) reexamination of the basic principle underlying insect metamorphosis, it had been completely overlooked that the Ca(2+)-pump (SERCA) blocker thapsigargin is a sesquiterpenoid that mimics the absence of JH in inducing apoptosis. In our opinion, being in the juvenile state is primarily controlled by endogenous FLS that participate in controlling the activity of Ca(2+)-ATPases in the sarco(endo)plasmic reticulum (SERCAs), not only in insects but in all eukaryotes. Understanding the control mechanisms of being in the juvenile state may boost research not only in developmental biology in general, but also in diseases that develop after the juvenile stage, e.g., Alzheimer's disease. It may also help to better understand some of the causes of obesity, a syndrome that holometabolous last larval insects severely suffer from, and for which they found a very drastic but efficient solution, namely metamorphosis.

Fatty aldehyde and fatty alcohol metabolism: review and importance for epidermal structure and function

Normal fatty aldehyde and alcohol metabolism is essential for epidermal differentiation and function. Long-chain aldehydes are produced by catabolism of several lipids including fatty alcohols, sphingolipids, ether glycerolipids, isoprenoid alcohols and certain aliphatic lipids that undergo α- or ω-oxidation. The fatty aldehyde generated by these pathways is chiefly metabolized to fatty acid by fatty aldehyde dehydrogenase (FALDH, alternately known as ALDH3A2), which also functions to oxidize fatty alcohols as a component of the fatty alcohol:NAD oxidoreductase (FAO) enzyme complex. Genetic deficiency of FALDH/FAO in patients with Sjögren-Larsson syndrome (SLS) results in accumulation of fatty aldehydes, fatty alcohols and related lipids (ether glycerolipids, wax esters) in cultured keratinocytes. These biochemical changes are associated with abnormalities in formation of lamellar bodies in the stratum granulosum and impaired delivery of their precursor membranes to the stratum corneum (SC). The defective extracellular SC membranes are responsible for a leaky epidermal water barrier and ichthyosis. Although lamellar bodies appear to be the pathogenic target for abnormal fatty aldehyde/alcohol metabolism in SLS, the precise biochemical mechanisms are yet to be elucidated. Nevertheless, studies in SLS highlight the critical importance of FALDH and normal fatty aldehyde/alcohol metabolism for epidermal function. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Farnesyl phosphatase, a Corpora allata enzyme involved in juvenile hormone biosynthesis in Aedes aegypti

Background

The juvenile hormones (JHs) are sesquiterpenoid compounds that play a central role in insect reproduction, development and behavior. The late steps of JH III biosynthesis in the mosquito Aedes aegypti involve the hydrolysis of farnesyl pyrophosphate (FPP) to farnesol (FOL), which is then successively oxidized to farnesal and farnesoic acid, methylated to form methyl farnesoate and finally transformed to JH III by a P450 epoxidase. The only recognized FPP phosphatase (FPPase) expressed in the corpora allata (CA) of an insect was recently described in Drosophila melanogaster (DmFPPase). In the present study we sought to molecularly and biochemically characterize the FPP phosphatase responsible for the transformation of FPP into FOL in the CA of A. aegypti.

Methods

A search for orthologs of the DmFPPase in Aedes aegypti led to the identification of 3 putative FPPase paralogs expressed in the CA of the mosquito (AaFPPases-1, -2, and -3). The activities of recombinant AaFPPases were tested against general phosphatase substrates and isoprenoid pyrophosphates. Using a newly developed assay utilizing fluorescent tags, we analyzed AaFPPase activities in CA of sugar and blood-fed females. Double-stranded RNA (dsRNA) was used to evaluate the effect of reduction of AaFPPase mRNAs on JH biosynthesis.

Conclusions

AaFPPase-1 and AaFPPase-2 are members of the NagD family of the Class IIA C2 cap-containing haloalkanoic acid dehalogenase (HAD) super family and efficiently hydrolyzed FPP into FOL. AaFPPase activities were different in CA of sugar and blood-fed females. Injection of dsRNAs resulted in a significant reduction of AaFPPase-1 and AaFPPase-2 mRNAs, but only reduction of AaFPPase-1 caused a significant decrease of JH biosynthesis. These results suggest that AaFPPase-1 is predominantly involved in the catalysis of FPP into FOL in the CA of A. aegypti.